Soon the cause of defending them and attacking the Shia-backed regime itself grew in popularity, and jihadis, young Sunni extremists from all around the globe, came to Syria. Today, these foreign fighters are said to number anywhere from 8,000, the estimate given by General Lloyd Austin, US Central Commander, to 12,000, and several of the groups are linked to al-Qaeda. Among the foreign jihadis now fighting in Syria there are believed to be 70 Americans, one of whom became a suicide bomber and blew himself up in May.

The refugee flows and the jihadi presence, which are both growing, constitute a threat to Syria, its neighbours, and both Europe and the United States. As to the US and Europe, the US Secretary of Homeland Security, Jeh Johnson, said in April that "Syria has become a matter of homeland security," and the Director of National Intelligence, James Clapper, said in January that one of the al-Qaeda-aligned Syrian jihadi groups "does have aspirations for attacks on the [American] homeland."  The European contingent is far larger than the American, perhaps 2,500 jihadis in all — with an estimated 700 from France and 400 from the UK as a minimum. It's a kind of jihadi EU, with representation from every member country in the ranks of the jihadi forces. New fighters, new training, new networks. "The Syrian war is therefore likely to be an incubator for a new generation of terrorists," one recent analysis concluded. While security officials are well aware of the threat, the flow of young men to fight in Syria and then back home continues. And the measure of the threat is that for thousands of these jihadis, "home" is not Karachi or Benghazi, but Marseilles or Leeds or Milwaukee.

But the jihadi threat to Syria's neighbours was always more immediate and it moved in June from spectre to reality. The al-Qaeda-linked terrorist group called ISIS, the Islamic State of Iraq and the Levant, was formed in Iraq in 2013 but began fighting inside Syria. It then moved east, recrossing the border, and conquering territory and cities in Iraq. Iraqis, including hundreds of thousands of civilians plus Iraqi soldiers trained and equipped at great expense by the US, fled. From Aleppo in Syria to Fallujah and then Mosul in Iraq, ISIS presents a challenge neither the West nor the government in Baghdad has yet been able to meet.

How has President Obama handled these dangers? The American government's Syria policy has been reactive and almost entirely humanitarian: not to deter or prevent violence or punish the regime, but to give succour to victims. The US has given large sums to alleviate the suffering, through aid to countries neighbouring Syria and to various UN and private agencies. Soon the total will reach $2 billion. But on the political and military front the Obama administration has been slow to lead or to act, and extremely wary of any role beyond providing humanitarian assistance.

In the early days of the conflict American policy discussions centred on how to persuade or force Assad to leave and how, afterwards, to build a stable democracy in Syria. Few analysts believe that internal peace and democracy are now a viable option for Syria or will be for many years to come, and the Obama administration appears to have given up on forcing Assad out. That led it to leap into the deal with Russia to remove Assad's chemical weapons, which had the side effect — no doubt calculated carefully in Moscow — of making Assad into America's partner. Simultaneously the Geneva negotiations sought a "political settlement", and the Americans strong-armed Syrian rebels into appearing at the talks. But the negotiations got nowhere, for the goal of Assad and his backers in Iran and Hezbollah (and Moscow) was to win the war, not negotiate a golden exile for him. The rebels could not gain in Geneva what they could not win on the battlefield, yet the Americans seemed absolutely unwilling to provide the support that would change the balance of forces on the ground.